Study of Energy Transfer and Triplet Exciton Diffusion in Hole‐Transporting Host Materials

Abstract

A device structure is used in which the hole‐transporting layer (HTL) of an OLED is doped with either fluorescent or phosphorescent emitters, that is, anode/HTL‐host/hole blocker/electron‐transporting layer/cathode. The HTL hosts have higher HOMO energy allowing holes to be transported without being trapped by dopant molecules, avoiding direct recombination on the dopant. The unconventional mismatch of HOMO energies between host and dopant allow for the study of energy transfer in these host/guest systems and triplet exciton diffusion in the HTL‐host layers of OLED devices, without the complication of charge trapping at dopants. The host materials examined here are tetraaryl‐p‐phenylenediamines. Data shows that Förster energy transfer between these hosts and emissive dopant in devices is inefficient. Triplet exciton diffusion in these host materials is closely related to molecular structure and the degree of intermolecular interaction. Host materials that contain naphthyl groups demonstrate longer triplet exciton diffusion lengths than those with phenyl substituents, consistent with DFT calculations and photophysical measurements.

Regioregular Phthalocyanines Substituted with Bulky Donors at Non‐Peripheral Positions

“…Compound 4 showedo ne reversible oxidation wave at + 0.77 Vv s. the ferrocenium/ferrocene( Fc + /Fc) couple. In comparison, 5 displayed two well-defined one-electron reversible redox couples at + 0.37 and + 0.69 Vv ersus Fc + /Fc corresponding to 5/ 5 + C and 5 + C/5 2 + .T he oxidation potentials of 4 and 5 were anodically shifteda sc ompared with the reference compounds, [37,38] indicating that the HOMO energy levels were stabilized by the introduction of electron-accepting nitrile groups.…”

“…/5 2+ . The oxidation potentials of 4 and 5 were anodically shifted as compared with the reference compounds, indicating that the HOMO energy levels were stabilized by the introduction of electron‐accepting nitrile groups.…”

Film thickness influence of dual iridium complex ultrathin layers on the performance of nondoped white organic light-emitting diodes

“…In the case of the high triplet energy of mCP (408 nm, 3.04 eV) [16] and a small amount of phosphorescent molecules, it's reasonable to postulate that mCP interlayer plays a role not only as a spacer between two phosphorescent ultrathin layers but also as an emitter in the devices. From Fig.…”

N,N-Diarylamino end-capping as a new strategy for simultaneously enhancing open-circuit voltage, short-circuit current density and fill factor in small molecule organic solar cells

“…29 As show in Fig. [19][20][21] Therefore, for these asymmetrical squaraine derivatives, the presence of N,N-diarylamino end-cappers could not endow them with better hole mobility. While for the six objective compounds, the hole mobility of their neat lms were calculated to be 0.56 Â 10 À5 to 5.42 Â 10 À5 cm 2 V À1 s À1 , and that of the composite lms is 0.44 Â 10 À5 to 1.77 Â 10 À5 cm 2 V À1 s À1 , both are comparable or even lower than that of ASQB samples.…”

“…16 Although ASQB displays a relatively low bandgap and good solubility owing to the presence of an electron-rich N,N-diisobutylamino group in it, the PCE of the corresponding BHJ-SMOSCs is unsatisfactory (1.54%), with low V oc of 0.75 V, J sc of 5.40 mA cm À2 , and FF of 0.38. 16 Moreover, recent research works have revealed that the replacement of N,Nalkylamino with N,N-diarylamino substituents in photovoltaic materials could not only lead to more intensied intermolecular p-p overlap that benets the broaden of the absorption spectra and the enhancement of charge-transporting properties in lm states, 19,20 hence higher J sc could be expected; but also endow these compounds with dropped HOMO energy levels, hence higher V oc could also be expected. 17,18 Additionally, by replacing the end-capper with a carbazolyl group, the resulting compound ASQC was found to show considerably lowered HOMO energy level, hence ASQC-based SMOSCs displays a very high V oc ; however, ASQC exhibits a higher energy bandgap with that of ASQB.…”